Sources tell CBS Sports that Manziel signed photographs and other memorabilia for an autograph broker in early January.

ESPN's "Outside the Lines" reports he was paid upwards of five figures to sign hundreds of items.

Officials at the NCAA reportedly grew suspicious when authenticated items signed by Manziel kept popping up on eBay.

The NCAA strictly prohibits athletes from "accepting any payment that promotes directly to the sale of a commercial product." Players violate those laws can be ruled ineligible.

Bruce Feldman, a writer with CBS Sports, says Texas A&M must now decide how to handle their star player. "If they play him, and the NCAA finds midseason that Johnny Manziel is ineligible, they would forfeit all of the games that Johnny Manziel had played in."

While this is the most severe allegation to hit Manziel, it's just the latest in a series of headline-grabbing events this offseason. Manziel has been spotted courtside at NBA games, and partying alongside pro athletes and celebrities.

In early July, he pleaded guilty to a misdemeanor charge following a bar fight, and later that week, he was asked to leave a football camp run by the Manning family.

Manziel said, "I'm continuing to grow up, I've made some mistakes and I'm absolutely manning up for those."

If the NCAA ruled Manziel ineligible this fall, the rising sophomore, who only spent one year on the national football stage, would likely see his NFL stock drop come draft time.

Feldman said, "NFL people wanted to see him play in 2013 to make sure, 'Hey, he's not a one-year wonder and if he can't play this year, there's even more uncertainty about him and can he be a guy NFL teams trust."

Neither Manziel nor Texas A&M have commented on the investigation, but in the meantime, the preseason for Aggies football begins Monday, and officials for the team say Manziel will practice.